2 files changed, 23 insertions, 3 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 85e80a57db29..6af555c1c42a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1221,9 +1221,7 @@ out:
  * The page has to be a nice clean _individual_ kernel allocation.
  * If you allocate a compound page, you need to have marked it as
  * such (__GFP_COMP), or manually just split the page up yourself
- * (which is mainly an issue of doing "set_page_count(page, 1)" for
- * each sub-page, and then freeing them one by one when you free
- * them rather than freeing it as a compound page).
+ * (see split_page()).
  *
  * NOTE! Traditionally this was done with "remap_pfn_range()" which
  * took an arbitrary page protection parameter. This doesn't allow
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 102919851353..fc65e87368b3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -752,6 +752,28 @@ static inline void prep_zero_page(struct page *page, int order, gfp_t gfp_flags)
                 clear_highpage(page + i);
 }
 
+#ifdef CONFIG_MMU
+/*
+ * split_page takes a non-compound higher-order page, and splits it into
+ * n (1<<order) sub-pages: page[0..n]
+ * Each sub-page must be freed individually.
+ *
+ * Note: this is probably too low level an operation for use in drivers.
+ * Please consult with lkml before using this in your driver.
+ */
+void split_page(struct page *page, unsigned int order)
+{
+        int i;
+
+        BUG_ON(PageCompound(page));
+        BUG_ON(!page_count(page));
+        for (i = 1; i < (1 << order); i++) {
+                BUG_ON(page_count(page + i));
+                set_page_count(page + i, 1);
+        }
+}
+#endif
+
 /*
  * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
  * we cheat by calling it from here, in the order > 0 path.  Saves a branch